(1) Field of the Invention
This invention relates to an input system comprising a resistance film touch panel and a device for detecting a pushed position of the touch panel, especially the one including a device for conducting the above detection by use of a change in electric potential which occurs when the touch panel is pushed.
(2) Description of the Prior Art
A simple input system including a touch panel and a detecting device for detecting a pushed position of the touch panel and for outputting a signal which indicates the two-dimensional coordinates of the position is widely used in combination with a character display device (CRT, LCD or PDP) or the like.
In an input system including a resistance film touch panel, a pushed position of the touch panel, namely, the position where two resistance films are contacted on each other, is detected based on the resistance value of the position--contrary to using capacitance.
Conventionally, two types of touch panels comprising resistance films have been offered: analog system touch panels and matrix system touch panels.
FIG. 1 shows an analog system touch panel. Two resistance films 91 and 92 are opposed to each other with a certain distance therebetween. The film 91 has outer connecting electrodes 93 and 94 along ends thereof, the ends extending along a Y axis; and the film 92 has outer connecting electrodes 95 and 96 along ends thereof, the ends extending along an X axis. In this construction, a pushed position A or B is detected by obtaining a resistance value r.sub.1 or r.sub.3 between the position A or B and the outer connecting electrode 95 and a resistance value r.sub.2 or r.sub.4 between the position A or B and the outer connecting electrode 93 and then converting the obtained resistance values into a voltage, which is outputted through the electrodes 94 or 96.
If the two points A and B are pushed simultaneously, r.sub.1 and r.sub.3 are connected in parallel and r.sub.2 and r.sub.4 are connected in parallel, thereby combined resistances are formed. The voltage is divided by the combined resistances, resulting in finding a position which is neither A nor B. Therefore, accurate detection of two pushed positions are impossible with this construction.
As shown in FIG. 2, a matrix system touch panel comprises a plurality of strip-like resistance films 101 arranged in parallel and a plurality of strip-like resistance films 102 arranged in parallel. The films 101 are extended along the X axis and the films 102 are extended along the Y axis, the films 101 and the films 102 having a certain distance therebetween. A pushed position is detected by finding out which films are contacted on each other by use of an appropriate scanner.
Since each film has a lead connected thereto, a great number of leads are necessary, which causes the wiring area to be too large compared with the detection area of the touch panel. Also required are a large number of input circuit components. These facts increase size of the system and manufacturing cost.
In an effort to minimize the number of the leads, touch panels are manufactured these days with various numbers of films for different usages. However, the necessity of manufacturing products with various numbers of films brings about another troublesome matter such as management of various components.